1. Field of the Invention
The present invention relates to a film forming apparatus and, more specifically, to a film forming apparatus which can perform a film forming process on a substrate to be processed without being affected by replacement of a substrate holder and by a process of removing a film accumulated on the substrate holder.
2. Description of the Related Art
In a production film forming apparatus for forming a film by moving a substrate holder in which a substrate is held, the film forming process is performed repeatedly while replacing a substrate in the substrate holder, having completed a predetermined film forming process, with a new substrate. While the film forming process is performed on the substrate, the film is accumulated not only on the substrate, but also on a substrate holding claw of the substrate holder and a portion therearound. Therefore, after repeated usage of the substrate holder, the film is thickly accumulated on the substrate holder, particularly on the substrate holding claw and the portion therearound, whereby a problem such that the quality of film formation on the substrate is lowered due to separation of the accumulated film is resulted.
In order to prevent or alleviate such a problem, a film forming apparatus which removes the film accumulated on the substrate holder in a film removing chamber provided separately so as to be branched from a path in the film forming apparatus in which a plurality of vacuum chambers are provided in series is disclosed in JP-A-2000-273615 (Patent Document 1). According to the Patent Document 1, an accumulated film on the surface of a single substrate holder is removed in a film removing chamber 41, as shown in FIG. 19.
Also, a film forming apparatus which removes an accumulated film on a substrate holder by providing a film removing mechanism on a homeward passage of a transfer mechanism provided between a load lock chamber and an unload lock chamber is disclosed in JP-A-2001-156158 (Patent Document 2).
However, with the film removing method described above, it is difficult to remove the accumulated film on the surface of the substrate holder efficiently without affecting a series of film forming process when the thickness of the accumulated film on the surface of the substrate holder increases. In particular, when a vertical magnetic recording system is employed for meeting the need of high density recording media in recent years, the film to be formed is thick, and hence the problem described above becomes obvious. Consequently, the necessity to perform replacement of the substrate holder frequently arises.
As described above, in a vertical magnetic recording film forming apparatus, the substrate holder is replaced every one or two days for preventing generation of particles caused by separation of the film accumulated on the substrate holding claw of the substrate holder or the portion therearound as matters stand.
In the film forming apparatus in the related art, substrate holders from which the accumulated film are removed and cleaned or new substrate holders (hereinafter, referred to as “new substrate holder”) are stored in a degasificated state in a vacuum heating degasificating furnace provided externally of the apparatus. After having retrieved, or during retrieval of, the substrate holders which need to be replaced from the apparatus, degasificated new substrate holders are retrieved once from the degasificating furnace into atmospheric air, and fed one by one to the film forming apparatus. However, there arrive problems such that the film forming apparatus having fed with the new substrate holders needs significant time for evacuating air until a predetermined pressure required for film formation is established, and that a significant time is required for re-degasification, which is generally required to be done again, in a heating chamber before actually starting production. In particular, when replacing a plurality of substrate holders, these problems become obvious.
In the film forming apparatus shown in Patent Document 1, removal of accumulated film can be performed without affecting the film forming process as long as the film on the substrate holder is thin. However, when a thick film is formed as described above, there arises a problem of timing for returning new substrate holders back to the path in the film forming apparatus, and hence the film forming process is disturbed and efficient production cannot be achieved.
In the film forming apparatus in Patent Document 2, the film removing mechanism is provided in the path in the film forming apparatus. Therefore, when the thickness of the film accumulated on the substrate holder increases, the time required for the entire film forming process is increased by time required for the processing in the film removing mechanism. As a consequence, productivity is lowered. Also, when attempt is made to perform film removing process without affecting the film forming process, the film cannot be removed satisfactorily.